When trying to play YouTube videos, after 1-2 minutes Opera become extremely slow, the video lag alot and when I try to close the tab it take 30-45 seconds to close, making Opera (12.16) use high CPU usage.

Also, it's not just playing videos, it also do that on playlist/search/channel/..., basically everything on YouTube.com. Just the main page YouTube.com take about 50% CPU while on the page.